Hi;I have 4000 series roomba and mainboard is fail. So i decided to use arduşno as mainbroad and i connected all sensors and motor to the arduino.

I have completed lots of part but have some questions;charging system. I am using orginal battery nicd, i remember that roomba open mosfets for charging than is starts with constant current charging. For my circuit can i use directly 1.25A fast charger with controlling voltage and temperature ? Or i can make basic circuit with lm317 and charge with 0,5A constant current and monitor temperature and voltage drops.

One description of NiCd charging procedure is at https://www.eeweb.com/blog/extreme_circuits/simple-nicd-battery-chargerLong superseded by NiMh for higher energy density, with a different charging procedure.The analog component procedure can be reproduced in software for the microcontroller. A number of small charging circuit boards are sold, some with microcontrollers. Batteries will typically be fused or polyfused for safety etc.

Programming your own system any type of battery can be used with appropriate algorithms. Neato systems contain more than one algorithm, with installation configuration commands to set battery type used.BatteryUniversity.com has a lot of info.